The present invention relates generally to catheters for performing medical procedures. More particularly, the present invention relates to reinforced intravascular catheters.
Intravascular catheters are currently utilized in a wide variety of minimally invasive medical procedures. Generally, an intravascular catheter enables a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient""s vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature.
Typically, the catheter enters the patient""s vasculature at a convenient location such as a blood vessel in the neck or near the groin. Once the distal portion of the catheter has entered the patient""s vascular system, the physician may urge the distal tip forward by applying longitudinal forces to the proximal portion of the catheter. For the catheter to effectively communicate these longitudinal forces, it is desirable that the catheter have a high level of pushability and kink resistance.
Frequently, the path taken by a catheter through the vascular system is tortuous, requiring the catheter to change direction frequently. It may also be necessary for the catheter to double back on itself. Physicians often apply torsional forces to the proximal portion of the catheter to aid in steering the catheter. To facilitate the steering process, it is desirable that an intravascular catheter have a relatively high level of torquability. Furthermore, in order for the catheter to conform to a patient""s tortuous vascular system, it is desirable that intravascular catheters be very flexible.
The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 5 mm. In light of the geometry of the patient""s body, it is desirable to combine the features of torqueabity, pushability, and flexibility into a catheter which is relatively long and has a relatively small diameter.
Ideally, the distal end of an intravascular catheter will be adapted to reduce the probability that the vascular tissue will be damaged as the catheter is progressed through the vascular system. This is sometimes accomplished by bonding or welding a relatively soft tip member to the distal end of an intravascular catheter.
After the intravascular catheter has been navigated through the patient""s vascular system so that its distal end is adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. One example of a diagnostic use for an intravascular catheter is the delivery of radiopaque contrast solution to enhance fluoroscopic visualization. In this application, the intravascular catheter provides a fluid path leading from a location outside the body to a desired location inside the body of a patient. In order to maintain a fluid path, it is desirable that intravascular catheters be sufficiently resistant to kinking. In addition, because such fluids are delivered under pressure, it is also desirable that intravascular catheters be sufficiently resistant to bursting or leaking.
One useful therapeutic application of intravascular catheters is the treatment of intracranial aneurysms in the brain. Approximately 25,000 intracranial aneurysms rupture each year in North America. An aneurysm which is likely to rupture, or one which has already ruptured, may be treated by delivering an embolic device or agent to the interior of the aneurysm. The embolic device or agent encourages the formation of a thrombus inside the aneurysm. The formation of a thrombus reduces the probability that an aneurysm will rupture. The formation of a thrombus also reduces the probability that a previously ruptured aneurysm will re-bleed. Thrombus agents which may be used include liquid thrombus agents such as cyanocrylate, and granulated thrombus agents such as polyvinyl alcohol. An additional type of thrombus agent which is frequently used is a tiny coil. Any of the thrombus agents described above may be delivered using an intravascular catheter.
When treating an aneurysm with the aid of an intravascular catheter, the catheter tip is typically positioned proximate the aneurysm site. The thrombus agent is then urged through the lumen of the intravascular catheter and introduced into the aneurysm. Shortly after the thrombus agent is placed in the aneurysm, a thrombus forms in the aneurysm and is shortly thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture. It is desirable that the lumen of the catheter provides a path for delivering embolic devices to an aneurysm. To this end, it is desirable that the pathway through the catheter have a low friction surface.
The blood vessels in the brain frequently have an inside diameter of less than 3 mm. Accordingly, it is desirable that intravascular catheters intended for use in these blood vessels have an outside diameter which allows the catheter to be easily accommodated by the blood vessel. The path of the vasculature inside the brain is highly tortuous, and the blood vessels are relatively fragile. Accordingly, it is desirable that distal portion of a catheter for use in the brain be adapted to follow the highly torturous path of the neurological vasculature.
As described above, it is desirable to combine a number of performance features in an intravascular catheter. It is desirable that the catheter have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also desirable that a catheter be relatively flexible, particularly near its distal end. The need for this combination of performance features is sometimes addressed by building a catheter which has two or more discrete tubular members having different performance characteristics. For example, a relatively flexible distal section may be bonded to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member.
The present invention relates generally to catheters for performing medical procedures. More particularly, the present invention relates to reinforced intravascular catheters. A catheter in accordance with the present invention includes an elongate shaft. A hub may be fixed to the proximal end of the elongate shaft. The elongate shaft is comprised of an inner tubular member having a first layer, a second layer, an outer surface, and a distal end.
A support member overlies at least a portion of the inner tubular member and conforms to the surface thereof. The support member has a first portion, a second portion, and a third portion. The first portion, second portion, and third portion each have a distal end and a proximal end. The first portion of the support member being disposed proximate the distal end of the inner tubular member. The first portion of the support member is comprised of at least one filament which is circumferentially disposed about the inner tubular member in a helical manner. The at least one filament generally conforms to the shape of the outer surface of the inner tubular member and forms a plurality of turns.
In a presently preferred embodiment, a ring is circumferentially disposed about the outer surface of the inner tubular member proximate the distal end thereof. In a presently preferred embodiment, the ring is comprised of a radiopaque material. In this presently preferred embodiment, the ring produces a relatively bright image on a fluoroscopy screen during a medical procedure. This relatively bright image aids the user of the catheter in determining the location of the distal end of the elongate shaft.
In one embodiment of the present invention, a distal portion of the at least one filament is disposed between the outer surface of the inner tubular member and the ring. Placing the distal portion of the filament in this position has the advantage of retaining the distal portion of the filament while the remainder of the filament is wound around the inner tubular member.
The second portion of the support member is circumferentially disposed about the inner tubular member, with its distal end proximate the proximal end of the first portion of the support member. In one embodiment of the present invention, the second portion of the support member is comprised of a lattice structure having a first layer, a second layer, and a third layer. Each layer being comprised of a plurality of turns, formed by at least one filament.
The third portion of the support member is comprised of a plurality of turns formed by at least one filament. In a presently preferred embodiment, the filaments forming the support member are all coextensive.
In a presently preferred embodiment, the elongate shaft includes a flare disposed proximate the proximal end thereof. The hub may be formed over the proximal end of the elongate shaft. In a presently preferred embodiment, the hub is formed using an insert molding process. In this presently preferred embodiment, the single filament includes a distal end and a proximal end. In this presently preferred embodiment, it is unlikely that the distal end of the filament will protrude through the outer layer of the catheter since the distal portion of the filament is retained by a ring, as described above. Likewise, it is unlikely that the proximal end of the filament will protrude from the catheter since a hub is disposed over the proximal end of the elongate shaft.
An outer layer overlays both the support member, and the inner tubular member. In a presently preferred embodiment, the material of the outer layer fills any interstitial spaces in the support member. Also in a presently preferred embodiment, the outer layer is comprised of a distal portion, a middle portion, and a proximal portion.
In one embodiment of the present invention, the proximal end of the distal portion of the outer layer is fused to the distal end of the middle portion thereof. Likewise, the proximal end of the middle portion of the outer layer is fused to the distal end of the proximal portion. In this presently preferred embodiment, the distal portion, the middle portion, and the proximal portion combine to form an outer layer which is substantially continuous.
In one aspect of the present invention, the outer diameter of the proximal portion of the outer layer is large enough to substantially cover the layers of the second portion of the support member. Likewise, in another aspect of the present invention, the outer diameter of the distal portion of the outer layer is large enough to substantially cover the first portion of the support member. In a presently preferred embodiment, the outer diameter of the distal portion of the outer layer is smaller than the outer diameter of the proximal portion of the outer layer. It may be appreciated that the single layer construction of the first portion of the support member facilitates having an outer diameter of the distal portion which is smaller than the outer diameter of the proximal portion.
In one embodiment of the present invention, the plurality of turns forming the first portion of the support member are disposed at a first pitch. Also in this embodiment, the turns of the second portion of the support member are disposed at a second pitch different than the first pitch. Finally, in this embodiment, the turns of the third portion of the support member are disposed at a third pitch. In a presently preferred embodiment, the pitches of the first, second, and third portions of the support member may be selected to impart desired performance characteristics upon the catheter. For example, the third pitch may be relatively coarse so that it does not hinder the formation of a flare at the proximal end of the elongate shaft.
In a presently preferred embodiment, the distal end of the first portion of the support member is disposed proximate the distal end of the elongate shaft. An atraumatic tip is formed from the inner tubular member and the outer layer. In this presently preferred embodiment, the atraumatic tip is disposed distally of the distal portion of the first portion of the support member. In this presently preferred embodiment, the atraumatic tip has a level of flexibility which makes it unlikely to damage the blood vessels of a patient.